Motor-control circuits



as, 1925. V. H. TODD MOTOR CONTROL CIRCUITS Filed June 24 1924 INVENTOR V/cior fi- 700 0 ORNEY Patented Apr. 13, i926.

UNITED STATES PATENT OFFICE.

VICTOR H. TODD, OI SUMMIT, NEW JERSEY, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

moroa-oon'raor. cmourrs.

Application filed June 24, 1924. Serial No. 722,172.

To all wit m it may aoncem:

Be it known that I, VIo'ron H. Tom), a citizen of the UnitedStates, and resident of Summit, in the county of Union and State of New Jersey, have invented a new and useful Improvement in Motor-Control Circuits, of which the following is a. specification.

My invention relates to motor-control circuits and particularly to control circuits for graphic-meter motors.

One object of my invention is to provide a circuit, of the above indicated character, that shall render a graphic-meter motor sensitively and accurately responsive to changes in the quanity being measured by the meter.

Another object of my invention is to provide means that shall eliminate arcing between the control contact members of a graphic-meter motor.

Another object of my invention is to provide a motor-control circuit that shall permit the motor to be operated on direct-current circuits and on alternating-current circuits of widely varying frequencies.

Another object of my invention is to provide a motor-control circuit that shall utilize dynamic braking to quicklystop rotation of the armature. I

A further object of my invention is to provide a motor-control circuit for graphicmeter motors that shall be simple and durable in construction and effective in its operation.

In graphic-meters practices, it is usual to provide a Kelvin balance that is actuated in accordance with volts, amperes, watts or any other quantity of a circuit that it is desired to measure.

To relieve the movable element of the balance of the necessity of moving a stylus or pen carriage, a pilot or control motor is ordinarily provided and the movable element is only required to open and close contact members to (lo-energize or reverse the field-winding current of the pilot motor in accordance with variations in the quantity being measured.

Trouble has been experience because of arcing at the contacts and because the inertia of the pilot motor armature has caused the pen carriage to over and under travel. Certain other faults have been inherent in meters of this type which rendered them troublesome and inaccurate.

In order to ensure suitable sensitivity of operation, that is, to ensure quick response of the pilot motor, it is necessary to have the clearances between the control contact members extremely slight; The least clearance at which good positive operation is obtainable is about two mils. The least practicable spacing has heretofore been about four mils. These small clearances, which have been used only in special cases requiring extreme sensitivity, have required extreme care in setting the 'gap to avoid shortcircuiting the stationary contacts with the moving contact. However, such settings have heretofore frequently caused blown fuses and burned armatures in the pilot or control motors.

In practicing my invention, I provide a pair of parallel-connected constantly-energized field-winding circuits, across equipotential points of which the control-motor armature is connected in the de-energized condition of the armature. A contact-making device so alternately connects the armature terminals to one end of the parallelfield-winding circuits as to alternately shunt a portion of each parallel leg of the field-' winding circuit. This operation causes a sufficient voltage drop across the armature to cause the latter to rotate in the one or the other direction. The eontact-making device is so connected to opposite terminals of the armature as to have no appreciable voltagedrop between a pair of its terminals in the de-energized condition of the motor, and is also connected to the motor field magnet windings through resistors, which absorb arcs between each contact member of said pair and a third contact member which alternately engages each of them.

Other resistors are provided and the circuits, including the armature and the field windings, are soarranged as to adapt the device for operation in direct-current circuits or in alternating-current circuits ,of widely varying frequencies, without arcing at the control contact members, and in an effective and quickly-responsive sensitive manner.

The single figure of the accompanying drawings is a diagrammatic view of the motor control circuit of my invention, the

Kelvin balance, the pen carriage and other form 'ot my invention, VZIIIOHS' modificaparts being omitted as not essential to an understanding thereof.

Between terminals 1 and 2, across whlch the actuating electromotive force is im pressed, are disposed a series resistor and two parallcl-field-rnagnet winding circuit paths 4 and 5. The path 4 comprises a resistor 7, a lield-1nagnet winding 8 and a noninductive resistor 9; and the path 5, similar- 1y, comprises a resistor 10, a field winding 11 4 points in .thc field-magnet-windmg circuits and a non-inductive resistor 12.

An armature 14 has terminals 15 and 16 that are respectively connected to equi-potcntial points 17 and 18 in the paths 4 and 5.

Stationary contact members 20 and 21 are connected to the armature terminals 15 and 16,- respectively, and a movable contact men1- ber 22, for a ternate engagement with the stationary contact members 20 and 21, is connects to a common terminal 23 of the resistors 7 and 10.

In operation, with electromotive forcebeing constantly impressed across the conductors 1 and 2 and the contact members 20, '21

and 22 in the positions illustrated inthe the armature 14 is stationary, be;

drawin cause tfiere is no voltage drop between the points 17 and 18. a

However, when the Kelvin balance, as above mentioned, responds to a changein the quantity being measured to move the contact number 22 .into engagement with one of the contact members 20 and 21, one of the resistors 7 and 10 is shunted to cause a drop of potential across the armature 14. This operation causes the armature to rotate.

When the movable contact member again moves to the disengaged position, the arc, which would ordinarily attempt to form,

is absorbed by the resistor 7 or the resistor 10 which had previously been shunted.

When the armature rotates under its own momentum, it generates a voltage which is short-circuited 10, to thus, bring the armature to a quick stop. This effect is known as dynamic braking.

The resistors 9 and 12 are provided to reduce the field magnet current and to thus effect the correct speed of the armature 14: when the actuating electromotive force is direct. When the actuating force alternates, at sixty cycles, the inductance of the field magnet windings 8 and 11 is ordinarily SlllfiClQIli; to ensure the correct speed.

It was found that the amount of resistance necessary in the field magnet circuit for various frequencies in the actuating force is practically constant, so an average value was'chosen, which permits the motor through the resistors 7 andto operate in circuits of widely varying frequencies without changing the resistors.

WVh1le-I have shown and described one tions and changes may be made without departingfrom the spirit and scope of the invention I desire, therfore, that only such limitations shall be placed thereon as are imposed by the 'prior art.

I claim as my invention:

' 1-. A motor-control circuit comprising parallel field-magnet-winding circuits, an armature connected between equi-potential ing the direction of rotation of the armature.

3. A motor-control circuit comprising parallel-field-magnet-winding circuits, an armature connected between equi-potential poi'nts'i'n thejfield-magnet winding circuits and means for alternately shunting a ortion of one of said field-magnet-win ing circuits and a portion of the other for re- 'versing the direction of rotation of the armature comprising a pair of contact members connected oiieyto each armature terminal and a third contactmember 'for alternate engagement with said pair of contact members and connected to one end of the parallel field-magnet circuit paths.

4-. A motor-control circuit comprising parallel field-magnet winding circuits, each comprising a field magnet winding and a. resistor, an armature connected across said circuits to positions between the resistor and the field magnet winding at each armature terminal, a pair of contact members connected one to each armature terminal and a thirdcontact member for alternate engagement-with said pair of contact members and connected to a common terminal of said-resistors. j

5. A motor-control circuit comprisin parallehfield-magnet winding circuits eac comprising a resistor, a field magnet winding and a second resistor arranged in the order named, an armature connected across said circuits between the'first resistor and the field-magnet winding at each armature terminal, a pair of contact members connect ed one to each armature terminal and a third contact member connected to a common terminal of said first resistor for alternate engagementwit-h the contact members of said pair. a

6. A motor control circuit comprising parallel field-magnet-winding circuits each comprising a resistor, a field magnet winding and a second resistor arranged in the 5 order named, an armature connected across said circuits between the first resistor and the field magnet winding it each armature terminal, a pair of contact members connected one to each armature terminal, a third contact member connected to a com- VICTOR H. TODD. 

